Agonistic and antagonistic effects of phthalates and their urinary metabolites on the steroid hormone receptors ERα, ERβ, and AR

Phthalate plasticizers have been reported to exert adverse effects via activation of the estrogen receptors ERα and ERβ and inhibition of the androgen receptor AR as molecular initiating events. After oral uptake, phthalates are metabolized to their corresponding monoesters and subsequently to oxidized phthalate monoester derivatives, which are in turn conjugated to glucuronic acid and finally excreted with the urine. In contrast to the parent phthalates, toxicological data regarding their primary and secondary metabolites are rare. The present study aimed at the characterization of potential endocrine effects of 15 phthalates and 19 phthalate metabolites by using reporter gene assays to monitor human ERα, ERβ, and AR activity. In these in vitro assays, the phthalates either stimulated or inhibited ERα and ERβ activity and inhibited AR activity, whereas the phthalate metabolites had no impact on the activity of these human hormone receptors. In contrast, the metabolites of di-(2-ethylhexyl) phthalate (DEHP) stimulated transactivation of the human peroxisome proliferator-activated receptors PPARα and PPARγ in analogous reporter gene assays, although DEHP itself did not activate these nuclear receptors. Therefore, primary and secondary phthalate metabolites appear to exert different effects at the molecular level compared to the parent compounds.